Tuned circuits for wireless receivers



July 27, 1943. A. H. COOiPER TUNED CIRCUITS FOR WIRELESS RECEIVERS FiledApril 21]., .1942

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70 AMPuF/m j 2: 721 AMPL mm INVENTOR. Air/we flaw/FY (oo s/ ATTORNEX iPatented July 2 1943 rime. c wwsae .BECEIV 1 .:Arthur JienryrCwpeBuchinghams ra llng E ici8:;Musica i1n mir es.if .L' e eH i ess ilan iasi n 1 -Applicatin:Aprilfil, 1942,'Se1 ial No. 439,350

tInGreati-Britain November-26,1940

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core or magnetic material isemployed inside a solenoid. This type oftuning inductance is most convenient for receivers covering only oneWave-' band; the addition of a further band leads either i to unsuitableratios of inductance to capacitance or else to the need for additionalcomponents. in receivers with bandspread tuning in some wavebands, thecomplications are likely to be serious. 7 I

The object of the present invention is to provide inexpensive wavebandspreading tuning means in a circuit employing permeability'tuning andinvolving he use of a vary few components.

According to the present invention a tuning circuit includes a singlepermeability tuned inductance which serves as the main tuning adjustmentmeans over frequencies in one tuning range and as a fine tuningadjustment means at frequencies higher than those in said tuning range.

A particular formof tunin circuit according to the invention includes asingle permeabilitytuned inductance shunted by a condenser which may bevariable, the frequency bandwidth covered by said inductance andcondenser being extensible by the addition of an alternative shuntcondenser, tuning to higher frequencies being effected by the additionof an inductance in shunt with the first inductance together with asuitable condenser or condensers in shunt, the arrangement being suchthat the permeability-tuned inductance operates as a fine tuning controlat the higher frequencies.

The tuning inductance can take care of the medium Waveband, for example,and can easily be arranged to cover the long waveband by the connectionof a suitable fixed condenser in shunt. On the short waves, the tuninginductance can be used to provide fine tuning in the spread bands byconnecting suitable values of fixed inductance and capacity in shunt soas to center the tuning range in the frequency ranges required, theratio of the fixed inductance to the fixed capacity being so chosen thatthe desired tuning, range is provided by the tuning inductance.

In order that the invention may be more clearly unde rst'ood and readily1 carried into efle'ctg al- 'ternative circuits embody g 'the inventionwill 1. wbe described in grea fdetail by accompanying drawing.

'diun1b 'adcastwav inductance required. yrrhe "shu'nt condenser Z'may saam i-semi 1 1 na zf ar'nple-with'refernbe ftofil igures j neat-re e; 1,the permeabilityto v. i r ,h e,

be fixed or variable. An extension orniawaimband over longer Wavelengthsis obtained Without the addition of variable inductance merely byarranging the wave change switch 3 to increase the capacity across thevariable inductance I by the substitution of a shunt condenser 4 for thecondenser 2. band over shorter wavelengths, again Without the use ofadditional variable inductances, is obtained by arranging the wavechange switch 3 to remove the shunt condensers 2 or i and to connect intheir place in parallel withthe variable induct-- ance l appropriatetuning elements such as inductance 5 and condenser E, or inductance! andcondenser 8. It will be clear that the provision of pairs of shuntcomponents provide suff cient degrees of freedom to allow both themid-frequency and the spread of each band to be given a any reasonablevalues.-

In a receiver with several bands, various components may with economy beshared between ,Wavebands; As an example, Figure 2 shows a method ofsharing condensers such as, could be v performed if the values ofcondenser 2 and condenser 8 in Figure 1 were found to be substantiallythe same, by splitting up the wave change switch Sinto two gangedsections 3 and 3a, one

selecting condensers and the other inductances. v 1 7 It will be seen inFigure 2 that by providing 'a a lead 9 from the end contact of theswitch contact arm 3 to the condenser 2 and by providing two deadcontacts for the first two positions of the V switch contact arm 3a, theequivalent arrange ment of Figure l is provided except that in theextreme right hand position of the switch contact arms, the condenser 2will be connected'across inductance 7, thus eliminating the condenser 8of Figure 1.

Variation of the position of the adjustable iron core cooperating withthe variable inductance I in Figure lior 2will tune the combination ofshunt inductance over a range adequate to cover one of the allocatedbroadcast bands, although the tuning is not linear.

The invention will be found to be of particular application to thedesign of low priced radio re-' Further, an extension of the wavetunedinductance, a condenser and a circuit com-' prising inductance and shuntcapacity, and means for selectively shunting the condenser or the lattercircuit across the permeability-tuned l inductance, the arrangementbeingsuchthat with,

the condenser shunting the permeability-tuned inductance the latterserves as the main tuning p means in one of the wave bands, and with thecircuit of the inductance wand shunt capacity shunting thepermeability-tuned inductance, the

latter serves as the fine tuning means in another,

higher frequency band.

2, A tunable circuit comprising a. single per meability-tuned inductanceand a shunt condenser of such values 'to tune the circuit over 7 one,wave band, said inductance serving as the tuning means in said band, acircuit corni prisinga fixedinductance and a shunt capacity, =tuneditothe mid-frequency of a band of higher frequencies than the first band,and means for substituting thelatter circuit for the first mentionedshunt condenser across the permeability- I tuned inductance, the latternow serving as the fine tuning means in the band ofhigher frequencies..

3. In a receiver; at least" one tunable circuit? ceiver through a bandof medium or broadcast 5 frequencies, and means for'replacing the shunt.

condenser with, a shunt circuit comprising an in ductance and a shuntcapacity which are tuned. to the mid-frequency of a higher frequencyband,. the permeability-tuned inductance effecting band.

10 spread tuningin said higher frequency band.

bility-tuned inductance, a, plurality of condensers: and a plurality offixed tuned. circuits, means for selectively connecting one of thecondensers or 5 one oi the fixed tuned circuits in shunt across thepermeability-tuned inductance, the values of said elements being suchthe receiver will be tuned to different frequency bands depending uponthe position of the selective means, the permeabilitytuned inductanceserving as the main tuning means when one of the condensers is shuntedthereacross, andsaid inductance serving a the fine tuning means forefiectin-g band spread tuning when one of the fixed tuned circuits isshunted g5 thereacross. I v

5. The invention as defined in claim 4 Where in at least one of thecondensers serves also as an element of the fixed tuned circuit.

30 V ARTHUR HENRY COOPER.

' 4'. In'amulti-band receiver, a single permea--

